The present invention relates to a method of producing an absorber material, the absorber material produced according to this method and a semiconductor array in a hermetically sealed housing in which the absorber material according to the present invention is arranged.
Open semiconductors are used in hermetically sealed housings, among other things. These housings contain, among other things, absorber material to absorb high frequencies occurring in the housing. Iron-filled silicone rubber is usually used as the absorber material.
The absorber material, i.e., the silicone rubber, is produced by addition crosslinking of a component A and a component B, where component A is a polydiorganosiloxane, in particular having the general formula xe2x80x94Oxe2x80x94SiR1R2CHxe2x95x90CH2 and component B is hydrogen siloxane, in particular having the general formula xe2x80x94Oxe2x80x94SiHCH3R where R, R1 and R2 are the same or different hydrocarbon radicals and/or H. the polydiorganosiloxane has accessible groups for crosslinking reactions, in particular vinyl groups which may be on the chain ends or incorporated into the chain. The addition-crosslinked silicone rubber used as the absorber material, in particular having the general formula xe2x80x94Oxe2x80x94SiR1R2xe2x80x94CH2xe2x80x94CH2xe2x80x94SiRCH3xe2x80x94Oxe2x80x94 is produced by addition of SiH groups to the vinyl groups bound to silicon in a process catalyzed by noble metals or noble metal compounds, in particular palladium, for example. SiH groups are supplied in the form of component B, i.e., in particular hydrogen siloxane, which functions as a plasticizer in the cured silicone rubber, i.e., in the absorber material, in production of the addition-crosslinked silicone rubber.
This absorber material emits molecular hydrogen over a period of time, in particular at high temperatures or under the influence of moisture. This hydrogen can escape from an open housing. In hermetically sealed housings, however, the hydrogen reacts with the semiconductor, thus shortening the lifetime of the component.
Therefore, it is known that an irreversible hydrogen getter can be used in the hermetically sealed housing. The hydrogen released is captured by the getter material, so that less hydrogen reaches the semiconductor. The hydrogen getter also has silicon as a carrier, the actual getter material being an organic compound that irreversibly takes up hydrogen through use of the catalyst palladium. Because of the high price of the hydrogen getter, it is not used in Germany in particular.
Another possibility of preventing the wear on the semiconductor due to the formation of hydrogen as described above is to temper the absorber material. According to this method, the iron-filled absorber material is tempered for 48 hours at 200xc2x0 C. before wear on the housing. Water and hydrogen are expelled from the absorber material, so that no hydrogen can evolve in the housing. However, one disadvantage is that this method is expensive and time consuming. Furthermore, the tempered absorber material must be stored under a protective gas and must not come into contact with atmospheric humidity. Finally, the mechanical properties of the absorber material are greatly impaired by tempering, and there are electric sealing problems in sealing the housing.
The present invention provides a method of producing an absorber material from a component A, in particular a polyorganosiloxane, preferably a polydiorganosiloxane, and a component B, in particular a hardener containing SiH, whereby in a first step of the method the SiH-containing hardener is added to the polyorganosiloxane in a reduced amount, and in a second step of the method a fully cured silicone rubber is obtained.
In conjunction with the present invention, a SiH-containing hardener is understood to refer to a compound that can crosslink polyorganosiloxanes using its SiH groups.
In conjunction with the present invention, a reduced amount of hardener containing SiH is understood to be an amount of hardener according to which little or no excess, i.e., uncrosslinked, silicon hydride groups are present in the fully cured, addition-crosslinked silicone rubber. The present invention provides in particular for the absorber material to be produced in such a way that the fully cured silicone rubber contains very little or no excess silicon hydride groups. This can be accomplished according to the present invention by increasing the curing temperature and/or adding a reduced amount of component B in comparison with the amount traditionally used in production of the absorber material.
The quantities of hardener traditionally recommended by the manufacturers of absorber materials lead to an excess of hardener in the addition-crosslinked silicone rubber, so that excess, uncrosslinked silicon hydride groups are present and react with water to form unwanted molecular hydrogen. This process can be represented by the following formulas: xe2x80x94[SiCH3HO]nxe2x80x94+nH2Oxe2x86x92xe2x80x94[SiCH3(OH)O]nxe2x80x94+nH2. The polymethylhydroxysiloxane formed in this reaction can also split off water by polycondensation with a vicinal molecule, thus sustaining the above-mentioned reaction, i.e., the release of hydrogen.
The quantities of hardener recommended by the manufacturers of these absorber materials may be reduced according to the present invention by approx. 40% to 50%. In particular, the present invention provides for the use of a ratio of polyorganosiloxane to SiH-containing hardener of 30:1 to 15:1, especially 26:1 to 18:1, in particular 90:35, 10:04, 9:04, 10:0.5 or 9:0.5 (amounts given in percent by weight).
The present invention has the advantage that hydrogen is no longer removed after being formed, but instead its formation is prevented from the beginning. The present invention has the advantage in particular that potential hydrogen emissions can be reduced by 95%, and no hydrogen can be detected at a sensitivity of 0.1 ppm when using absorber materials either with or without iron powder. Up to this temperature, it is certain that no hydrogen is released that could damage the semiconductors. The absorber material can be produced less expensively because of the small amount of hardener used, among other things. In addition, time is saved in production, especially with regard to the known tempering method. Finally, the mechanical requirements made of the absorber material produced according to the present invention, such as thermal stability, Shore A hardness, etc., are met in an advantageous manner.
In an especially preferred embodiment of the present invention, the above-mentioned method is carried out in such a way that a temperature of 140 to 180xc2x0 C., preferably 150xc2x0 C., is maintained over a period of 0.5 to 3 hours, preferably one hour, in the second step of the method, i.e., in the final curing. The curing temperature according to the present invention which is increased in comparison with the curing temperature of approx. 80xc2x0 C. traditionally used leads to a further reduction in the formation of hydrogen.
The present invention also relates to a method of producing an absorber material from a component A, in particular a polyorganosiloxane such as polydiorganosiloxane, and a component B, in particular a hardener containing SiH, whereby in a first step of the method the SiH-containing hardener is added to the polyorganosiloxane, and then in a second step of the method, final curing is performed at a temperature of 140xc2x0 C. to 180xc2x0 C., preferably 150xc2x0 C., over a period of 0.5 to 3 hours, preferably one hour, yielding a fully cured, addition-crosslinked silicone rubber. Thus, according to the present invention, it is possible to reduce hydrogen emissions by the measure of adding the hardener in a reduced amount and also by the measure of increasing the final curing temperature. A combination of both measures is of course also possible as described here. Both measures, either alone or in combination, lead to the production of an improved addition-crosslinked silicone rubber which is characterized in that it has essentially no free SiH groups.
The present invention also relates to the above-mentioned methods, whereby the addition-crosslinked silicone rubber is filled with iron powder. This is advantageous in particular because iron powder itself is a very good hydrogen getter.
According to an especially preferred embodiment of the present invention, hydrogen siloxane, preferably having the empirical formula CH3xe2x80x94[SiHCH3O]xxe2x80x94CH3 where xxe2x89xa71, is used as the hardener.
The present invention of course also relates to an absorber material made of an addition-crosslinked silicone rubber with and without iron powder produced according to one of the methods mentioned above. The absorber material, i.e., the addition-crosslinked silicone rubber according to the present invention is characterized in that it contains essentially no free, i.e., uncrosslinked, SiH groups.
The present invention also relates to a semiconductor array including a semiconductor arranged in a hermetically sealed housing, with an absorber material according to the present invention being arranged in the housing as a damping material.
Additional advantageous embodiments of the present invention are derived from the subordinate claims.